Shaped aperture in enameled sheet metal

ABSTRACT

A shaped aperture in a porcelain enameled sheet metal panel for receiving and securing a thread forming or sheet metal screw. The metal panel is dimpled inwardly surrounding the aperture with an inside radius at the dimple of about two times the metal thickness. A continuation of the dimple defines a truncated cone having a base diameter sufficient to provide clearance around the screw outer diameter and the screw receiving aperture, defined by the plane of truncations, having a diameter about equal to the root diameter of the screw and with the normal distance between the plane of the panel and the truncating plane being on the order of 0.9 to 1.5 times the outer diameter of the screw. As the screw is received within the aperture some enamel is crushed and separated from the metal by the thread. The separation of the enamel from the metal is limited to the area immediately adjacent the aperture and within the base diameter.

United States Patent [191 Bebinger Oct. 7, 1975 SHAPED APERTURE IN ENAMELED SHEET METAL [75] Inventor: Jack E. Bebinger, Columbus, Ohio [73] Assignee: White-Westinghouse Corporation, Cleveland, Ohio [22] Filed: June 24, 1974 [21] Appl. No.: 482,195

[52] US. Cl. 52/758 D; 220/64 [51] Int. Cl. F16B 5/02 [58] Field of Search 52/758 D, 758 F, 614, 623,

[56] References Cited UNITED STATES PATENTS 1,411,184 3/1922 Rosenberg 52/758 F Primary Examiner-Werner H. Schroeder Assistant Examiner-Wayne L. Shedd 7 flununa 44 swwmv o [57] ABSTRACT A shaped aperture in a porcelain enameled sheet metal panel for receiving and securing a thread forming or sheet metal screw. The metal panel is dimpled inwardly surrounding the aperture with an inside radius at the dimple of about two times the metal thickness. A continuation of the dimple defines a truncated cone having a base diameter sufficient to provide clearance around the screw outer diameter and the screw receiving aperture, defined by the plane of truncations, having a diameter about equal to the root diameter of the screw and with the normal distance between the plane of the panel and the truncating plane being on the order of 0.9 to 1.5 times the outer diameter of the screw. As the screw is received within the aperture some enamel is crushed and separated from the metal by the thread. The separation of the enamel from the metal is limited to the area immediately adjacent the aperture and within thebase diameter.

5 Claims, 3 Drawing Figures SHAPED APERTURE IN ENAMELED SI-[EET METAL BACKGROUND OF THE INVENTION ample of a prior art enameled sheet metal aperture can i be found in U.S. Pat. No. 2,293,399, and an example of an aperture in non-enameled sheet metal construction can be found in U.S. Pat. No. 1,411,184. Another patent of general interest is U.S. Pat. No. 2,266,609.

SUMMARY OF THE INVENTION An enameled sheet metal dishwasher tub is'shown having a shaped aperture which confines the separation or chipping of the enamel from the metal to the area around the edge of the screw receiving aperture when a thread forming or sheet metal screw is received and secured therein. The aperture is defined by the plane of truncation of a truncated cone, with the cone being a continuation of an inwardly extending dimple and wherein the following general parameters are applicable: The bend radius of the dimple is limited to about twice the thickness of the sheet metal and the included angle of the cone is about 45; the depth of the shaped aperture (i.e. axial distance from the plane of the panel to the plane of truncation) is about 0.9 to 1.5 times the outside diameter of the screw thread, and the diameter of the base of said truncated cone is about 1.2 times the outside diameter of the screw thread providing a clearance therebetween. With such relationships, the separation of the enamel from the sheet metal is limited to an area adjacent the edge of the aperture and within that portion of the shaped aperture describing the truncated cone.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an enameled sheet metal dishwasher tub showing the environment of the invention;

FIG. 2 is an enlarged sectional view taken along line IIIl of FIG. 1;

FIG. 3 is a sectional view comparable to that of FIG. 2 but of a prior art arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT The dishwasher tub shown in FIG. 1 includes a front flange 12 substantially surrounding on three sides, an opening 14. Extending rearwardly from the distal edge of the front flange 12 is a stub flange 16. The front flange and stub flange aid in mounting the tub 10 within the dishwasher wrapper, a portion of the top panel of which is shown in FIG. .1 and is indicated by reference numeral 18. The tub 10 is secured to the top panel 18 by a series of screws one of which is shown at 20. The screw 20, as shown in FIG. 2 passes through the panel 18 to threadably engage the front flange 12. Screw 20 is preferably a sheet metal screw however, it is to be understood that a'thread forming screw could also be used. The front flange as well as the entire tub 10 is comprised of a sheet metal base 22 covered with a porcelain enamel 24.

Before describing the present invention as shown in FIG. 2, a brief discussion of a typical prior art arrangement, shown in FIG. 3, and some of the problems associated therewith would serve to better emphasize the improvement of the present invention. Like elements in FIGS. 2 and 3 carry the same reference character. As is known in the art when a metal sheet 22 having an aperture 25 formed therein and a porcelain coating 24 exv tending to the edge of the aperture, is baked, a phenomena known as bumoff occurs around the edges of the aperture. To avoid this, a procedure known as brushing is employed wherein the dried or bisque porcelain is removed from the metal for a distance 26 extending back from the perimeter of the aperture before the sheet is fired. However, this procedure often results 'in a buildup 27 or an increase in thickness of the enamel adjacent the edge of the enamel at the brushed aperture. When the panel 18 is secured to the flange 12 by the screw 20, this buildup at 27 causes non-uniform compression of the enamel layer 24 which results in chipping or cracking at 28 of the enamel layer. Another disadvantage of this arrangement is that the screw 20 expands and burrs the sheet metal 22 around the aperture as it cuts the thread, leaving the metal at the edge of the aperture thickened as indicated at 30. As the panel is drawn downwardly in FIG. 3 by the screw 20, the thickened metal at 30 causes a bending type loading of the enamel 24 which also is a contributing cause of uncontrolled chipping in that it can extend outwardly for some distance from the aperture.

FIG. 2 illustrates an embodiment of the invention which overcomes the deficiencies associated with the prior art arrangement of FIG. 3. The invention as shown in FIG. 2 utilizes confinement of the deforming or flexing effects resulting from the screw forces to also confine the chipping in an area removed from the plane defining the ground surface of the panel. Thus, an inwardly (i.e. away from the enamel coating) extending dimpled hole 31 is formed in the tub according to the following parameters. The dimpled hole 31 is comprised of an inwardly bent annular portion 32 surrounding the aperture 25. The annular portion 32 is continued inwardly to form a truncated cone section 34 with the plane of truncation defining the aperture 25. The diameter of the opening 36 which is the point of transition from the radius 32 to the truncated cone 34, or the base of the cone, is larger than the major diameter 38 of the screw 20 by a ratio of about 1.2 to l. The annular portion 32 has a bend radius 40 of approximately twice the thickness of the sheet metal 22. The truncated cone 34 has an included angle 42 of about 45. The depth 44 of the dimpled hole measured from the outer surface of the enameled porcelain 24 to the plane of truncation of the cone is approximately 0.9 to 1.5 times the major diameter 38 of screw 20. The diameter 46 of the aperture 25 is about equal to the root diameter 48 of the threads of screw 20.

As the screw 20 is driven into the enameled hole, conforming to the parameters described above, it forces the bottom of the truncated cone 34 to expand or distend crushing the porcelain 24 as it cracks away from the expanding metal around the aperture 25 limiting separation of the porcelain 24 from the metal 22 to an area surrounding the hole within the truncated cone 34. Although it is not certain, it is believed this limited separation is the result of several factors, one being that the annular portion 32 restricts the expansion of the metal 22 to within the truncated cone 34 precluding strain of the porcelain 24 above the diameter of the opening 36. To achieve this effect it is therefore critical to have a clearance between the screw threads and the diameter of the opening 36. The ratio of 1.2 to 1 described above provides sufficient clearance but larger ratios would accomplish the same result. Another factor believed to contribute to controlled chipping is that the porcelain 24 is stronger in compression than in tension. As the threads of screw engage the metal in the truncated cone 34 the aperture is distended causing flexure of the cone 34. This flexure exerts a tensile force on the porcelain and the porcelain breaks at the point of highest tension which appears to be at the diameter of the opening 36. In the flat hole, FIG. 3 type arrangement, the metal around the aperture 25 tends to expand and because of the cohesion between the metal and the porcelain adjacent the hole, the porcelain is compressed as the metal expands shearing a chip at an uncontrolled breaking point.

Brushing around the aperture of the FIG. 2 arrangement is not required and even if the enamel 22 webs over the aperture 25 the controlled chipping displayed will not be effected. In addition, if buildup would occur at the edge of the aperture 25 in the FIG. 2 arrangement, the non-uniform loading situation which contributed to the uncontrolled chipping in FIG. 3 arrangement is avoided. The area in FIG. 3 immediately adjacent the screw, being the area loaded most heavily in compression, in the FIG. 2 arrangement is no longer loaded in compression because the annular portion 32 removes the enameled porcelain 24 from contact with panel 18 in the area immediately adjacent the screw 20.

I claim:

1. A shaped aperture in a porcelain enameled sheet metal panel of predetermined thickness, said shaped aperture having a configuration particularly adapting it for receiving and threadably securing therein a screw having a predetermined root diameter and outside thread diameter subsequent to being enameled and confining any enamel cracking upon receipt of said screw to within said shaped aperture, and wherein said shaped aperture is formed from the metal panel and comprises:

an inwardly bent annular portion having a bend radius of less than about twice the thickness of said panel;

a truncated cone portion extending inwardly from said inwardly bent annular portion;

said truncated cone portion terminating in an aperture at the plane of truncation with said aperture having a diameter on the order of said root diameter of said screw, and said portion further having a base diameter at its juncture with said annular portion, with said base diameter greater than said outside thread diameter; wherein said screw is received in said shaped aperture and displaces the material immediately surrounding said aperture at the plane of truncation outwardly exerting a tensile force upon the enamel covering the cone portion and wherein said bend radius rigidifies the junction of said cone with the surrounding panel to prevent tensile forces extending into said panel to limit the fracture of said enamel to said cone portion.

2. The generally dimple shaped aperture of claim 1 wherein: said inwardly bent annular portion is of sufficient inward curvature to remove said porcelain enameled sheet metal from compression loading in the area immediately adjacent said screw.

3. The generally dimple shaped aperture of claim 1 wherein: said truncated cone shape has an included angle of about 45.

4. The generally dimple shaped aperture of claim 1 wherein: said truncated cone shape has a height in the range of about 0.9 to 1.5 times said outside thread diameter said height measured from the plane of truncation to the plane of the surface of said procelain enameled panel.

5. In a dishwasher tub formed from a porcelain enameled sheet metal panel of a given thickness, a generally dimple shaped aperture therein for receiving and secur ing a screw having an outer thread diameter and a root diameter, said generally dimple shaped aperture comprising an inwardly bent annular portion with a bend radius of about twice said metal thickness, and an inward continuation of the dimple defining a truncated cone shape with the plane of truncation defining a hole having a diameter about equal to said root diameter of said screw, said generally dimple shaped aperture having a diameter of opening dimension, defined as the di ameter of the base portion of said cone shape, about 1-1/5 times greater than said outer thread diameter, said cone shape having an included angle of about 45, and a height in the range of about 0.9 to 1.5 times said outer thread diameter. 

1. A shaped aperture in a porcelain enameled sheet metal panel of predetermined thickness, said shaped aperture having a configuration particularly adapting it for receiving and threadably securing therein a screw having a predetermined root diameter and outside thread diameter subsequent to being enameled and confining any enamel cracking upon receipt of said screw to within said shaped aperture, and wherein said shaped aperture is formed from the metal panel and comprises: an inwardly bent annular portion having a bend radius of less than about twice the thickness of said panel; a truncated cone portion extending inwardly from said inwardly bent annular portion; said truncated cone portion terminating in an aperture at the plane of truncation with said aperture having a diameter on the order of said root diameter of said screw, and said portion further having a base diameter at its juncture with said annular portion, with said base diameter greater than said outside thread diameter; wherein said screw is received in said shaped aperture and displaces the material immediately surrounding said aperture at the plane of truncation outwardly exerting a tensile force upon the enamel covering the cone portion and wherein said bend radius rigidifies the junction of said cone with the surrounding panel to prevent tensile forces extending into said panel to limit the fracture of said enamel to said cone portion.
 2. The generally dimple shaped aperture of claim 1 wherein: said inwardly bent annular portion is of sufficient inward curvature to remove said porcelain enameled sheet metal from compression loading in the area immediately adjacent said screw.
 3. The generally dimple shaped aperture of claim 1 wherein: said truncated cone shape has an included angle of about 45*.
 4. The generally dimple shaped aperture of claim 1 wherein: said truncated cone shape has a height in the range of about 0.9 to 1.5 times said outside thread diAmeter said height measured from the plane of truncation to the plane of the surface of said procelain enameled panel.
 5. In a dishwasher tub formed from a porcelain enameled sheet metal panel of a given thickness, a generally dimple shaped aperture therein for receiving and securing a screw having an outer thread diameter and a root diameter, said generally dimple shaped aperture comprising an inwardly bent annular portion with a bend radius of about twice said metal thickness, and an inward continuation of the dimple defining a truncated cone shape with the plane of truncation defining a hole having a diameter about equal to said root diameter of said screw, said generally dimple shaped aperture having a diameter of opening dimension, defined as the diameter of the base portion of said cone shape, about 1-1/5 times greater than said outer thread diameter, said cone shape having an included angle of about 45*, and a height in the range of about 0.9 to 1.5 times said outer thread diameter. 